This invention relates to a device and a method for use in detecting a surface roughness of an object surface of an object. It is to be noted throughout the instant specification that the object to be detected may be a magnetic recording medium, a semiconductor wafer, a photomask blank, a photomask, or the like, although the following description will be directed mainly to the magnetic recording medium used in a magnetic recording/reproducing device.
Heretofore, it has been required to extremely flatten a surface of a magnetic recording medium, such as a magnetic disk, which has a disk shaped substrate of, for example, glass, aluminum, and a magnetic film formed on the disk shaped substrate. This is because protrusions, recessions, and/or damages, which determine a surface roughness on a surface of the magnetic recording medium, bring about bad influences on recording or reproducing information signals recorded on the magnetic recording medium and often give rise to destruction of a magnetic recording/reproducing device.
More specifically, a head slider is used on recording on or reproducing from the magnetic recording medium and is caused to float above the magnetic recording medium during the recording or the reproducing, with a gap left between the magnetic recording medium and the head slider on the order of submicron and to travel all over the magnetic recording medium. Under the circumstances, when large protrusions or recessions are present on a surface of the magnetic recording medium, the recording or reproducing often becomes difficult at positions of such protrusions and recessions. On the other hand, the head slider may collide with the protrusions and, as a result, may bring about destruction of the head slider and the magnetic recording medium.
To this end, the surface roughness of the magnetic recording medium should be precisely tested or monitored after the magnetic recording medium is manufactured. This applies to a photomask, a semiconductor wafer, and so on.
Herein, it is to be noted that the magnetic recording medium is usually tested by a glide test and a certifying test so as to investigate the surface roughness and to insure a magnetic characteristic of the magnetic recording medium, respectively. In any event, such glide and certifying tests should be quickly made over a whole surface of the magnetic recording medium that is very wide.
Practically, a wide surface, such as the surface of the magnetic recording medium can not be tested by using a probe for touching the surface from a point to another point or a needle for measuring a tunnel current because use of such a probe or a needle undesirably lengthens a test time.
Taking this into consideration, a method for the glide test has been proposed which uses a glide head including a head slider and a piezo electric element attached to the head slider. In this case, the glide head travels above the surface of the magnetic recording medium. With this structure, an electric signal which corresponds to the surface roughness of the magnetic recording medium can be extracted from the piezo electric element.
However, it should be considered that the piezo electric element itself has a size and a weight which are not negligible in comparison with those of the head slider. This means that a flight state of the head slider does not always faithfully represent a state of the surface of the magnetic recording medium, which makes a measurement error large. As a result, the measurement error is not negligible when the piezo electric element is used.
In addition, it is a recent trend that the head slider becomes small in size. Therefore, such a small head slider makes it difficult to mount the piezo electric element.
An alternative method has been also proposed which uses a glide head including a head slider, a support arm attached to the head slider to support the head slider, and an acoustic emission (AE) sensor mounted on the support arm. With this structure, no problem takes place as regards a size and a weight of the acoustic emission (AE) sensor because the AE sensor is not directly attached to the head slider and is remote from the head slider.
However, a movement or vibration of the head slider is indirectly transmitted through the support arm to the AE sensor. Therefore, the vibration of the head slider can not be faithfully transmitted to the AE sensor. This means that a measurement error is included in a measurement result of the AE sensor.
Furthermore, the certifying test has been also conducted by the use of a head slider which is different from that used in the glide test. The head slider for the certifying test has a magnetic head for recording and reproducing information signals on or from the magnetic recording medium. In other words, the magnetic head for the certifying test should have recording and reproducing functions.
From this fact, it is readily understood that different head sliders should be prepared so as to make the glide and the certifying tests.